Changes in gene expression associated with the differentiation of murine embryonal carcinoma cells to extraembryonic endoderm will be investigated by direct electrophoretic analysis of the H1 histones and nonhistone, nuclear-associated proteins and cellular hybridization experiments. The extinction of one of five subtypes of the H1 histones may be correlated with the differentiation of embryonal carcinoma cells to parietal endoderm. The distribution of H1 subtypes in the chromatin of embryonal carcinoma cells and endodermal cells will be investigated. Activities responsible for the extinction of embryonal carcinoma functions and the possible activation of endodermal functions in cellular hybrids between embryonal carcinoma cells and parietal endodermal cells will be studied in hybrids between human choriocarcinoma cell lines and murine embryonal carcinoma cells. Parietal endodermal cells will be fractionated, concentrated, and microinjected into embryonal carcinoma cells to determine if activities can be detected which will cause embryonal carcinoma cells to differentiate. (K)